Generally, to insert a catheter into a blood vessel, the vessel is initially identified via aspiration by a syringe with an attached hollow needle by a technique commonly referred to as the Seldinger technique. When blood is drawn into the syringe, this indicates that the vessel has been found. The syringe is then disengaged from the needle and the needle lumen is occluded to prevent a possible air embolism and/or to prevent excessive bleeding. Thereafter, confirmation of needle placement in the vein or artery can be assured by haemodynamic monitoring or checking for pulsatile blood flow. Then, a thin guide wire is introduced, typically through the syringe needle or other introducer device, into the interior of the blood vessel. The needle/introducer device is then withdrawn leaving the guide wire within the vessel, wherein the guide wire projects outwardly beyond the surface of the skin.
At this point, several options are available to a physician for catheter placement. The simplest is to pass the catheter directly into the blood vessel directly over the guide wire. The guide wire is then withdrawn, leaving the catheter in position within the vessel. Correct catheter tip placement may then be verified by x-ray procedures. However, this technique is only possible in cases where the catheter is of a relatively small diameter and not significantly larger than the guide wire. If the catheter to be inserted is significantly larger than the guide wire, a dilator device may be first passed over the guide wire to enlarge the insertion hole. The catheter is then introduced over the dialator/guide wire, and the guide wire and dilator are withdrawn.
The technique may be rather routine and straightforward in cases where the patient's blood vessel is near the surface of the skin and is directly visible. If one is inserting a catheter into such vessels, the path of the catheter quickly becomes invisible without special equipment like x-ray and radio opaque coating on the catheter. For newborns use of x-ray is often not advised. Fortunately the elderly and newborns have fairly translucent skin and this fact is taken advantage of with the present invention. Even more, once the elusive vessel is found, the insertion and steering of the catheter is usually a blind procedure with verification of correct catheter tip placement only confirmed after the fact by radiographic methods.
Given this, there is a need for a technique continuously in real time to visualize and/or identify the relative location of non-visible blood vessels for initial catheter entry and subsequent real-time visualization while guiding the catheter for correct tip placement. Furthermore, there are circumstances where other tubes may need to be placed within the body and be guided without the need to special technologies such as x-rays.
Finally, it may be useful to have a technique which can locate blood vessels by non interventional detection of blood constituents.